OBJECTIVES: Alzheimer’s disease (AD), the most common form of dementia, is a degenerative disorder of the brain that leads to memory loss. Oxidative stress is a hallmark of AD. This study aims to identify the genetic alterations of AD by using the conventional cytogenetic technique by Trypsin G- banding and molecular analysis of presenilin 1 (PS1) genotype by PCR. The role of selected ions related to energy metabolism as a consequence of oxidative stress in the deterioration accompanied in AD patients were also analyzed. METHODS: The present study includes 49 AD patients and the subjects were categorized in two groups (14 Early-Onset AD) patients and (31 Late- Onset AD) patients, in order to investigate the possible cytogenetic and molecular damage. The gels were developed by staining with silver nitrate. RESULTS: The Late- Onset AD patient shows higher total CA level when compared to Early-Onset AD patient. A comparison of the frequencies for PS1 genotypes among the Early-Onset AD and Late- Onset AD subjects demonstrated a significant difference between the two groups. CONCLUSIONS: The strong association of PS1 with Late- Onset AD patients called attention to the importance of genetic studies in AD and the possible roles of PS1 in the progression of this disease. Based on the contributing effects of PS1 in AD pathogenesis, targeting PS1 may provide new opportunities for AD therapeutic strategies. Key Words: Early-Onset Alzheimer's disease patient, Late- Onset Alzheimer's disease patients, PS1, PCR – RFLP